Methods and systems for leaching a metal-bearing material using hydrogen peroxide and citric acid

ABSTRACT

A system and method for recovering a metal value from a metal-bearing material is provided. The method includes agglomerating the metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to form an agglomerated metal-bearing material. The method further includes leaching the agglomerated metal-bearing material with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution. The method further includes recovering the metal value from the pregnant leaching solution to produce the raffinate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S. Provisional Patent Application Ser. No. 63/246,046 filed Sep. 20, 2021, entitled “Methods and Systems for Leaching a Metal-Bearing Material Using Hydrogen Peroxide and Citric Acid,” the disclosure of which is incorporated herein by reference in its entirety for all proposes.

FIELD OF INVENTION

The present invention generally relates to methods and systems for recovering metal values from metal-bearing materials and, more specifically, to leaching methods and systems using hydrogen peroxide and citric acid.

BACKGROUND

Heap leaching provides a low-cost method of extracting metal values from relatively low-grade metal-bearing materials and has found particular application in the processing of metal-bearing ores. Generally, in traditional heap leaching operations, an ore is mined, crushed, and then transported to a heap location where it is stacked onto an impervious pad. In some operations, the crushed ore goes through a particle size enhancement process called agglomeration to improve leaching efficiency before it is transported to the heap. A suitable acidic solution is dispensed onto the heap, and the resulting leach solution trickles slowly through the heap under the force of gravity to the pad. This pad typically has a sloped base to allow the solution to flow into collection drains for further processing, such as by a conventional, solvent extraction/electrowinning (SX/EW) process or a direct electrowinning (DEW) process.

Once ores have been subject to the energy intensive processes of crushing and agglomeration, a high percentage of the contained valuable metal can be extracted by existing leaching methods. While these methods are relatively effective at metal extraction, implementing improvements to traditional processing techniques to increase extraction efficiency is economically advantageous. An improvement of leaching efficiency based on existing leaching methods may entail using reagents other than acids in the leaching solution. Various additives have been proposed for the purpose of improving the effectiveness of heap leaching operations, but many of these can create operational issues or, under certain conditions, pose risks to worker health and safety. For example, the addition of chloride to leach solutions had been found to improve extraction of copper from sulfide minerals, but the chloride solutions are prone to cause the corrosion of metals, particularly stainless steel. This can necessitate the use of costly alloys for hydrometallurgical plant construction. Another class of reagents that have been proposed are the thiocarbonates—including thiourea. Thiourea compounds have been associated with elevated epidemiological impacts and thus would require the adoption of proactive occupational health measures to ensure public health and safety impacts would be mitigated. Accordingly, there is a need for leaching methods and systems with improved occupational safety, efficiency, and reduced environmental impact. Introducing hydrogen peroxide and citric acid to the leaching solution results in increased extraction efficiency with little adverse environmental effects. Additionally, heap leach operations that run at above-ambient temperatures are more efficient and, when hydrogen peroxide is added in the agglomeration step of a traditional, sulfuric acid-based leach operation, the exothermic reaction naturally generates heat. This natural reaction provides a lower-cost alternative to traditional heat-addition methods which require external heat sources to raise heap temperature.

SUMMARY

In one aspect of the present invention, a method for recovering a metal value from a metal-bearing material is provided. The method includes agglomerating the metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to form an agglomerated metal-bearing material. The method further includes leaching the agglomerated metal-bearing material with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution. The raffinate may also contain hydrogen peroxide. The method further includes recovering the metal value from the pregnant leaching solution to produce the raffinate.

In various embodiments, the agglomeration may comprise resting the metal-bearing material in contact with the agglomeration solution for about 0 to about 8 days, for about 0 to about 4 days, or for a duration on the order of at least 1 day. In various embodiments, the agglomeration solution may comprise a concentration of hydrogen peroxide in the range of about less than about 10% by weight, about 1 to about 6% by weight, or on the order of about 4 to about 6% by weight.

In various embodiments, the leaching may comprise resting the agglomerated metal-bearing material in contact with the leaching solution for about 0 to about 4 days, for about 0 to about 2 days, or for a duration on the order of at least 1 day. In various embodiments, the leaching solution may comprise a concentration of citric acid on the order of less than about 40 g/l, less than about 20 g/l, or in the range of about 0.5 g/l to less than about 10 g/l.

In various embodiments, the metal value may comprise copper, nickel, zinc, silver, gold, germanium, lead, arsenic, antimony, chromium, molybdenum, rhenium, tungsten, iron, ruthenium, osmium, cobalt, rhodium, iridium, palladium, platinum, uranium, or rare earth metals. In various embodiments, the metal-bearing material comprises an ore, a concentrate, or a process residue.

In various embodiments, the method may further comprise forming at least a portion of a heap with the agglomerated metal-bearing material after the step of agglomerating. In various embodiments, the leaching may comprise leaching the heap with the leaching solution. In various embodiments, the metal recovery may comprise a solvent extraction and electrowinning (SX/EW) process, or a direct electrowinning (DEW) process. In various embodiments, the agglomeration may comprise curing the metal-bearing material in the agglomeration solution to form a cured metal-bearing material.

In another aspect of the present invention, a method for recovering a metal value from a metal-bearing material is provided. The method includes agglomerating the metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to form an agglomerated metal-bearing material. The method further includes forming at least a portion of a heap with the agglomerated metal-bearing material. The method further includes leaching the heap with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution. The method further includes recovering the metal value from the pregnant leaching solution to produce the raffinate.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present invention, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein:

FIG. 1 is a flow diagram illustrating a leaching method in accordance with various embodiments of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. The description of specific examples indicated in various embodiments of the present invention are intended for purposes of illustration only and are not intended to limit the scope of the invention disclosed herein. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.

Furthermore, the detailed description of various embodiments herein makes reference to the accompanying drawing figures, which show various embodiments by way of illustration. While the embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that logical and mechanical changes may be made without departing from the spirit and scope of the present invention. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, steps or functions recited in descriptions of any method, system, or process may be executed in any order and are not limited to the order presented. Moreover, any of the step or functions thereof may be outsourced to or performed by one or more third parties. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component may include a singular embodiment.

The present invention generally relates to methods and systems for recovering metal values from metal-bearing materials and, more specifically, to leaching methods and systems using hydrogen peroxide and citric acid. Various embodiments of the present invention provide a method for recovering metal values through agglomerating a metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to produce an agglomerated metal-bearing material, leaching the agglomerated metal-bearing material with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution, and recovering the metal value from the pregnant leaching solution to produce the raffinate. In accordance with the various embodiments of the present invention, the disclosed process increases metal value yield compared with convention methods and systems. Other advantages and benefits of the various embodiments of the present invention include that the disclosed process has little adverse environmental effects. For example, one of the reagents used, hydrogen peroxide, is converted into water during the process, while the other reagent, citric acid, is reused throughout the leach cycle with little impact on the environment.

In accordance with an exemplary embodiment of the present invention, a method for recovering a metal value from a metal-bearing material includes the steps of: (i) agglomerating a metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to produce an agglomerated metal-bearing material; (ii) leaching the agglomerated metal-bearing material with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution; and (iii) recovering the metal value from the pregnant leaching solution to produce the raffinate. In an aspect of this exemplary embodiment, the agglomeration may include resting the metal-bearing material in the agglomeration solution for a duration on the order of at least 1 day. In another aspect of this exemplary embodiment, the leaching may include resting the agglomerated metal-bearing material in the leaching solution for a duration on the order of at least 1 day.

In an another exemplary embodiment, a process for recovering a metal value from a metal-bearing material includes the steps of: (i) agglomerating a metal-bearing material with an agglomeration solution, which contains a raffinate and hydrogen peroxide, to produce an agglomerated metal-bearing material; (ii) forming a heap or a portion of a heap with the agglomerated material-bearing material; (iii) leaching the heap with a leaching solution, which contains the raffinate and citric acid, to produce a pregnant leaching solution; and (iv) recovering the metal value from the pregnant leaching solution to produce the raffinate.

Examples of metal values include, but are not limited to, copper, nickel, zinc, silver, gold, germanium, lead, arsenic, antimony, chromium, molybdenum, rhenium, tungsten, iron, ruthenium, osmium, cobalt, rhodium, iridium, palladium, platinum, uranium, or rare earth metals. More preferably, the metal values can be copper, nickel, and/or zinc. Most preferably, the metal value is copper.

Referring now to FIG. 1 , a metal leaching method 100 is illustrated according to various embodiments of the present invention. In accordance with various aspects of the embodiments, a metal-bearing material 102 may be provided for processing from which copper and/or other metal values may be recovered. The metal-bearing material 102 may be an ore, a concentrate, a process residue, or any other material from which metal values may be recovered. Metal values, such as those described herein, may be recovered from the metal-bearing material 102. In an aspect of the present invention, the metal-bearing material 102 may comprise a refractory metal sulfide.

In accordance with various embodiments, the metal-bearing material 102 may comprise chalcocite, pyrite, chalcopyrite, arsenopyrite, bornite, covellite, digenite, cobaltite, enargite, galena, greenockite, millerite, molybdenite, orpiment, pentlandite, pyrrhotite, sphalerite, stibnite, and/or any other suitable metal-bearing ore material. Preferably, the metal-bearing material 102 may comprise primary or secondary sulfides such as chalcocite, bornite, pyrite, or chalcopyrite, or a blend of such mineral species.

Various aspects and embodiments of the present invention, however, prove especially advantageous in connection with the recovery of copper from copper sulfide ores, such as, for example, chalcopyrite (CuFeS₂), chalcocite (Cu₂S), bornite (Cu₅FeS₄), covellite (CuS), enargite (Cu₃AsS₄), digenite (Cu₉S₅), and mixtures thereof. Thus, the metal-bearing material 102 may be a copper ore or concentrate, and preferably, is a copper sulfide ore or concentrate.

The metal-bearing material 102 may comprise ore in a number of states. Before an ore deposit is mined, the ore is said to be in an in-situ state. During mining, the metal-bearing material 102 may progress through multiple states as it is harvested, collected, transported, and processed. For example, the metal-bearing material 102 as harvested at the mining site may often be referred to as run of mine (or “ROM”) ore. ROM ore may be produced by, for example, blasting, open pit mining, and other surface and subterranean ore extraction techniques. As such, ROM ore includes ore of various sizes from ore as small as powder up to and including boulders.

In an aspect of the present invention, all or a portion of the metal-bearing material 102 may be further processed via size classification and/or crushing to achieve a desired particle size distribution, such that, substantially all of the particles are of a size to allow effective agglomeration of the metal-bearing material 102 and allow for optimal economic recovery of the contained metal values. The agglomerating process 110 may cure the metal-bearing material 102 to form a cured metal-bearing material.

In accordance with various embodiments of the present invention, the metal-bearing material 102 has a particle distribution of any combination of particle distributions. The particle distribution may have a combination of fine and coarse particles. Any particle distribution that maximizes agglomeration and/or curing, and metal recovery is useful. The conditions and parameters of the metal leaching method 100 disclosed herein may be adjusted to achieve an optimized result for leaching and metal recovery.

In accordance with various embodiments, the metal-bearing material 102 is subjected to an agglomerating process 110 to produce an agglomerated metal-bearing material 104. In various embodiments, the agglomerating process 110 may include applying an agglomeration solution to the metal-bearing material 102. In various embodiments, the agglomeration solution may include a raffinate 112 and an oxidizing agent. In various embodiments, the oxidizing agent may oxidize a metal component in the metal-bearing material 102 and agglomerate the metal-bearing material 102. In various embodiments, the oxidizing agent may include hydrogen peroxide, or any other suitable and known oxidant. In various embodiments, the agglomerating process 110 may combine the metal-bearing material 102 with the raffinate 112 and hydrogen peroxide to form the agglomerated metal-bearing material 104. In various embodiments, the agglomerating process 110 may cure the metal-bearing material 102 in the agglomeration solution to form a cured metal-bearing material. In various embodiments, curing may render the metal-bearing material 102 amenable to a subsequent leaching process.

As will be appreciated by those skilled in the art, the raffinate 112 and hydrogen peroxide may be mixed prior to combination with the metal-bearing material 102. In an exemplary embodiment, a raffinate provided from any other metal recovery process (not shown) may be used to form the agglomerated metal-bearing material 104. In various embodiments, the raffinate 112 may be an aqueous product of a solvent extraction process, such as, for example, a conventional solvent extraction/electrowinning (SX/EW) process, or a direct electrowinning (DEW) process. In various embodiments, the raffinate 112 may comprise water and acid.

In an aspect of the invention, the agglomerating process 110 may involve the metal-bearing material 102 being combined with the raffinate 112 and hydrogen peroxide in an agglomeration drum. An agglomeration drum may be any suitable agglomeration drum known in the art. In accordance with an exemplary embodiment, the raffinate 112 and hydrogen peroxide may be combined with the metal-bearing material 102 within the agglomeration drum. The quantity of the raffinate 112 and the quantity of hydrogen peroxide in the agglomeration solution may vary with respect to the type and/or quantity of metal-bearing material 102 used. In this regard, the raffinate 112 may be mixed with a certain quantity of hydrogen peroxide to form an agglomeration solution and the agglomeration solution may be optimized during the agglomerating process 110. The metal-bearing material 102 is mixed with the raffinate 112 and hydrogen peroxide in the agglomeration drum to produce the agglomerated metal-bearing material 104. The agglomerating process 110 may include the blending of coarse portions and fine portions of the metal-bearing material 102, in order to maximize metal recovery while maintaining heap permeability in heap leaching.

In an aspect of the invention, the agglomeration solution may include a certain concentration of hydrogen peroxide. In various embodiments, the concentration of the hydrogen peroxide in the agglomeration solution may be adjusted to achieve an optimized result for agglomeration and metal recovery. In various embodiments, the minerology of the ore may consume a portion of the hydrogen peroxide during the agglomeration process 110. In these embodiments, as the actual concentration of hydrogen peroxide in the agglomeration solution will be lower than the added concentration, a more highly concentrated addition of hydrogen peroxide in the initial agglomeration solution is necessary to obtain the desired actual—lower—hydrogen peroxide concentration. In various embodiments, the size of the crushed ore may vary. In these embodiments, the finer crushed material will require a lower concentration of added hydrogen peroxide while coarser material necessitates the addition of a higher hydrogen peroxide concentration. In various embodiments, the agglomeration solution may comprise a concentration of hydrogen peroxide in the range of less than about 10% by weight, 1 to about 6% by weight, or on the order of about 4 to about 6% by weight.

In various embodiments, the addition of hydrogen peroxide to the raffinate 112 o form an agglomeration solution may produce heat in the agglomeration solution. In various embodiments, heat generated by adding hydrogen peroxide to the raffinate 112 to form an agglomeration solution may increase a temperature of the agglomeration solution. In various embodiments, heat generated by adding hydrogen peroxide to the raffinate 112 to form an agglomeration solution may increase a temperature of the agglomeration solution by about 10 to about 13° C. In various embodiments, the agglomerating process 110 may be carried out in an agglomeration solution with a temperature of about 28 to about 35° C.

In an aspect of the invention, the agglomerating process 110 may comprise resting the metal-bearing material 102 in the agglomeration solution for a certain period of time. In various embodiments, the certain period of time may be adjusted to achieve an optimized result for agglomeration and metal recovery. In various embodiments, the metal-bearing material 102 may rest in the agglomeration solution for any duration in the range of about 0 to about 8 days. In various embodiments, the metal-bearing material 102 may rest in the agglomeration solution for any duration in the range of about 0 to about 4 days. In various embodiments, the metal-bearing material 102 may rest in the agglomeration solution for any duration on the order of at least 1 day.

In an aspect of the invention, the agglomerated metal-bearing material 104 may be subjected to a leaching process 120 to produce a pregnant leaching solution 106. In various embodiments, the leaching solution used in the leaching process 120 may comprise the raffinate 112 and a chelating agent. In various embodiments, the chelating agent may have affinity with the metal value and form a water-soluble metal chelate complex with the metal value to keep the metal value in an aqueous solution. In various embodiments, the chelating agent may comprise citric acid, ethylenediamine-N,N′-disuccinic acid (“EDDS”), or any other suitable and known chelating agent. In various embodiments, the leaching solution may comprise water and acid.

In an aspect of the invention, the leaching solution may include a certain concentration of citric acid. In various embodiments, the concentration of citric acid in the leaching solution may be adjusted to achieve an optimized result for leaching and metal recovery. In various embodiments, the leaching solution may comprise a concentration of citric acid on the order of less than about 40 g/l, less than about 20 g/l, or in the range of about 0.5 g/l to less than about 10 g/l.

In an aspect of the invention, a leaching solution may include hydrogen peroxide. In various embodiments, hydrogen peroxide may be added to other reagents, such as the raffinate 112 and citric acid, to form a leaching solution before the leaching process 120. In various embodiments, hydrogen peroxide may be added to a leaching solution during the leaching process 120. In various embodiments, hydrogen peroxide may be added to a leaching solution at various time intervals during the leaching process 120.

In various embodiments, an addition of hydrogen peroxide to other reagents to form a leaching solution before the leaching process 120 may generate heat in the leaching solution. In various embodiments, an addition of hydrogen peroxide to a leaching solution during the leaching process 120 may generate heat in the leaching solution. In various embodiments, heat generated by adding hydrogen peroxide to other reagents to form a leaching solution before the leaching process 120 may increase a temperature of the leaching solution. In various embodiments, heat generated by adding hydrogen peroxide to other reagents to form a leaching solution before the leaching process 120 may increase a temperature of the leaching solution by about 10 to about 15° C. In various embodiments, heat generated by adding hydrogen peroxide to a leaching solution during the leaching process 120 may increase a temperature of the leaching solution. In various embodiments, heat generated by adding hydrogen peroxide to a leaching solution during the leaching process 120 may increase a temperature of the leaching solution by about 10 to about 15° C. In various embodiments, the leaching process 120 may be carried out in a leaching solution with a temperature of about 28 to about 35° C.

In an aspect of the invention, the leaching process 120 may comprise applying the leaching solution to the agglomerated metal-bearing material 104 and resting the agglomerated metal-bearing material 104 in the leaching solution for a certain period of time. In various embodiments, the certain period of time may be adjusted to achieve an optimized result for leaching and metal recovery. In various embodiments, the agglomerated metal-bearing material 104 may rest in the leaching solution for any duration in the range of about 0 to about 4 days. In various embodiments, the agglomerated metal-bearing material 104 may rest in the leaching solution for any duration in the range of about 0 to about 2 days. In various embodiments, the agglomerated metal-bearing material 104 may rest in the leaching solution for any duration on the order of at least 1 day.

In an aspect of the invention, the leaching process 120 may comprise heap leaching. In various embodiments, the heap leaching may comprise stacking or forming the agglomerated metal-bearing material 104 into a heap or a portion of a heap. In various embodiments, the heap leaching may comprise leaching the heap with the leaching solution after the heap is formed. In another aspect of the invention, the leaching process 120 may comprise any other known leaching method, such as column leaching or shake flask leaching.

In an aspect of the invention, the pregnant leaching solution 106 may be subjected to a metal recovery process 130 to produce the metal value 108 and the raffinate 112. In various embodiments, the metal recovery process 130 may comprise a direct electrowinning (DEW) process. In another exemplary embodiment, the metal recovery process 130 may comprise a solvent extraction and electrowinning (SX/EW) process.

In various embodiments, the raffinate 112 may be recirculated and reused in the metal leaching method 100. In various embodiments, the raffinate 112 may be reused in the agglomerating process 110 as a component of the agglomeration solution. In various embodiments, the raffinate 112 may be reused in the leaching process 120 as a component of the leaching solution. In various embodiments, hydrogen peroxide may be added to the raffinate 112 to form an agglomeration solution to agglomerate the metal-bearing material 102. In various embodiments, citric acid may be added to the raffinate 112 to form a leaching solution to leach the agglomerated metal-bearing material 104.

In an aspect of the invention, part or all of the metal leaching method 100 may be carried out under a certain pressure and temperature. In various embodiments, the agglomerating process 110, leaching process 120, and metal recovery process 130 may be carried out under a certain pressure and temperature. In various embodiments, the pressure and/or temperature may be adjusted to achieve an optimized result for agglomeration, leaching, and/or metal recovery.

In various embodiments, the agglomerating process 110, leaching process 120, and/or metal recovery process 130 may be carried out under an atmospheric pressure. In various embodiments, the agglomerating process 110, leaching process 120, and/or metal recovery process 130 may be carried out under another pressure. In various embodiments, the agglomerating process 110, leaching process 120, and/or metal recovery process 130 may be carried out under an ambient temperature, such as 20-22° C. In various embodiments, the agglomerating process 110, leaching process 120, and/or metal recovery process 130 may be carried out under another temperature, such as 23-60° C.

The Examples set forth herein are illustrative of exemplary embodiments of the present invention. The process, conditions and parameters reflected therein are intended to exemplify various aspects of the invention and are not intended to limit the scope of the claimed invention.

EXAMPLE 1

A specimen of copper-containing ore was subject to a leaching method disclosed in the present invention. The ore contained 0.01% of chalcocite, 0.12% of chalcopyrite, 0.01% of copper-bearing clays, 0.01% of copper-bearing biotite, and 0.01% of other types of copper-bearing materials. First, 25 grams of the ore was added to 15 grams agglomeration solution. The agglomeration solution contains a raffinate produced from a copper leaching process and hydrogen peroxide. Hydrogen peroxide may be omitted from the agglomeration solution in certain leaching operations to show its agglomeration effect. The concentration of hydrogen peroxide in the agglomeration solution was either 0% or 1%. Next, the ore was allowed to rest in the agglomeration solution for 23 hours at a certain temperature as described below under an atmospheric pressure to produce an agglomerated ore. Following that, the agglomerated ore was leached in a 250 mL shake flask for 24 hours under an atmospheric pressure at 20-22° C. to produce a pregnant leaching solution. The leaching solution contains the same raffinate and citric acid. Citric acid may be omitted from the leaching solution in certain leaching operations to show its leaching effect. The concentration of citric acid in the leaching solution is either 5 g/l or 10 g/l. The pregnant leach solution was separated from the ore by a filtration process and assayed to determine extracted metal concentration. The filtered ore was then washed, and the wash water was also assayed.

The following four groups of leaching operations were carried out, as listed in Table 1. Except those conditions and reagents described below and listed in Table 1, the four groups of leaching operations were conducted under the same conditions with the same reagents. Group 1 is a leaching method without using hydrogen peroxide in the agglomeration solution or citric acid in the leaching solution. Group 1 was carried out to show the agglomeration effect of hydrogen peroxide and leaching effect of citric acid and its agglomeration process was at 20-22° C. Group 2 used 1% hydrogen peroxide in the agglomeration solution but used no citric acid in the leaching solution. Group 2 was carried out at to show the leaching effect of citric acid and its agglomeration process was at 20-22° C. Group 3 used 10 g/l citric acid in the leaching solution but used no hydrogen peroxide in the agglomeration solution. Group 3 was carried out to show the agglomeration effect of hydrogen peroxide and its agglomeration process was at 20-22° C. Group 4 used 1% hydrogen peroxide in the agglomeration solution and 10 g/l citric acid in the leaching solution. Group 4 was carried out to show both the agglomeration effect of hydrogen peroxide and leaching effect of citric acid and its agglomeration process was at 20-22° C. As illustrated in Table 1, the leaching results showed that the combination of hydrogen peroxide and citric acid significantly enhanced the copper recovery. The leaching method in Group 4, which used both hydrogen peroxide and citric acid, resulted in a copper recovery of 49.27% compared with 6.36% of copper recovery from the leaching method in Group 1 which used neither hydrogen peroxide nor citric acid.

TABLE 1 Conditions and Cu Recovery Rates of Four Groups of Leaching Operations Group No. H₂O₂ (%) Citric Acid (g/l) Cu Recovery (%) 1 0 0 6.36 2 1 0 38.28 3 0 10 5.89 4 1 10 49.27

EXAMPLE 2

Another specimen of the same copper-containing ore used in Example 1 was subject to a leaching method disclosed in the present invention. The experimental conditions, methodology, and tested reagents were identical to those in Example 1 apart from a variation in leaching temperature, hydrogen peroxide concentration in the agglomeration solution, and citric acid concentration in the leaching solution, as described below. The agglomeration solution contained a raffinate produced from a copper leaching process and hydrogen peroxide. The concentration of hydrogen peroxide in the agglomeration solution was 4%. The ore rested in the agglomeration solution for 23 hours at either 20-22° C. or 35° C. under an atmospheric pressure to produce an agglomerated ore. The agglomerated ore was then leached in a 250 mL shake flask for 24 hours at either 20-22° C. or 35° C. under an atmospheric pressure to produce a pregnant leach solution. The leaching solution contained the same raffinate and citric acid. The concentration of citric acid in the leaching solution was either 0.5g/l or 1.0 g/l. The pregnant leach solution was separated from the ore by a filtration process and assayed to determine extracted metal concentration. The filtered ore was then washed, and the wash water was also assayed.

The following four groups of leaching operations were carried out, as listed in Table 2. All four groups used a hydrogen peroxide concentration of 4% in the agglomeration solution and, except those conditions and reagents listed in Table 2, the four groups of leaching operations were conducted under the same conditions with the same reagents. Groups 1 and 2 used 0.5 g/l of citric acid and were conducted at 20-22° C. and 35° C. respectively to show the agglomeration effect of hydrogen peroxide and the leaching effect of citric acid at lower and higher temperatures. Groups 3 and 4 used 1.0 g/l of citric acid and were conducted at 20-22° C. and 35° C. respectively to show the agglomeration effect of hydrogen peroxide and the leaching effect of citric acid and lower and higher temperatures. As illustrated in Table 2, the leaching results showed that higher temperature processing enhanced copper recovery. The leaching method in Group 2, which was conducted at 35° C., resulted in a copper recovery of 47.89% compared with 44.04% from the leaching method of Group 1, which was conducted at 20-22° C.

TABLE 2 Conditions and Cu Recovery Rates of Four Groups of Leaching Operations Group No. Citric Acid (g/l) Temperature (° C.) Cu Recovery (%) 1 0.5 20-22 44.04 2 0.5 35 47.89 3 1.0 20-22 46.84 4 1.0 35 48.43

As discussed above, the present invention includes a metal leaching method utilizing hydrogen peroxide and citric acid to improve the efficiency of metal extraction operations. The present invention has been described with reference to various exemplary embodiments. However, many changes, combinations, and modifications may be made to the exemplary embodiments without departing from the scope of the present invention. For example, the various components may be implemented in alternate ways. These alternatives can be suitably selected depending upon the particular application or in consideration of any number of factors associated with the operation of the system. In addition, the techniques described herein may be extended or modified for use with other metal extraction processes. These and other changes or modifications are intended to be included within the scope of the present claims.

The present invention has been described above with reference to a number of exemplary embodiments. It should be appreciated that the particular embodiments shown and described herein are illustrative of the invention and its best mode and are not intended to limit in any way the scope of the invention as set forth in the claims. Those skilled in the art having read this disclosure will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope of the present invention. For example, various aspects and embodiments of this invention may be applied to recovery of metals other than copper, such as nickel, zinc, cobalt, and others. Although certain preferred aspects of the invention are described herein in terms of exemplary embodiments, such aspects of the invention may be achieved through any number of suitable means now known or hereafter devised. Accordingly, these and other changes or modifications are intended to be included within the scope of the present invention.

It is believed that the disclosure set forth above encompasses at least one distinct invention with independent utility. While the invention has been disclosed in the exemplary forms, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. Equivalent changes, modifications and variations of various embodiments, materials, compositions, and methods may be made within the scope of the present invention, with substantially similar results. The subject matter of the inventions includes all novel and non-obvious combinations and sub combinations of the various elements, features, functions, and/or properties disclosed herein.

Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element or combination of elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all the claims or the invention. Many changes and modifications within the scope of the instant invention may be made without departing from the spirit thereof, and the invention includes all such modifications. Corresponding structures, materials, acts, and equivalents of all elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claim elements as specifically claimed. The scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given above. 

What is claimed is:
 1. A method for recovering a metal value from a metal-bearing material, comprising: agglomerating the metal-bearing material with an agglomeration solution to form an agglomerated metal-bearing material, wherein the agglomeration solution includes a raffinate and hydrogen peroxide; leaching the agglomerated metal-bearing material with a leaching solution to produce a pregnant leaching solution, wherein the leaching solution includes the raffinate and citric acid; and recovering the metal value from the pregnant leaching solution to produce the raffinate.
 2. The method of claim 1, wherein the agglomerating comprises resting the metal-bearing material in the agglomeration solution for about 0 to about 8 days.
 3. The method of claim 1, wherein the agglomerating comprises resting the metal-bearing material in the agglomeration solution for about 0 to about 4 days.
 4. The method of claim 1, wherein the agglomerating comprises resting the metal-bearing material in the agglomeration solution for a duration on the order of at least 1 day.
 5. The method of claim 1, wherein the agglomerating is performed in an agglomeration solution with a temperature of about 28 to about 35° C.
 6. The method of claim 1, wherein the agglomeration solution comprises a concentration of hydrogen peroxide in the range of about less than about 10% by weight.
 7. The method of claim 1, wherein the agglomeration solution comprises a concentration of hydrogen peroxide of about 1 to about 6% by weight.
 8. The method of claim 1, wherein the agglomeration solution comprises a concentration of hydrogen peroxide of about 4 to about 6% by weight.
 9. The method of claim 1, wherein the leaching comprises resting the agglomerated metal-bearing material in the leaching solution for about 0 to about 4 days.
 10. The method of claim 1, wherein the leaching comprises resting the agglomerated metal-bearing material in the leaching solution for about 0 to about 2 days.
 11. The method of claim 1, wherein the leaching comprises resting the agglomerated metal-bearing material in the leaching solution for a duration on the order of at least 1 day.
 12. The method of claim 1, wherein the leaching is performed in a leaching solution with a temperature of about 28 to about 35° C.
 13. The method of claim 1, wherein the leaching solution comprises a concentration of citric acid of less than about 40 g/l.
 14. The method of claim 1, wherein the leaching solution comprises a concentration of citric acid of less than about 20 g/l.
 15. The method of claim 1, wherein the leaching solution comprises a concentration range of citric acid of from about 0.5 g/l to less than about 10 g/l.
 16. The method of claim 1, wherein the metal value comprises copper, nickel, zinc, silver, gold, germanium, lead, arsenic, antimony, chromium, molybdenum, rhenium, tungsten, iron, ruthenium, osmium, cobalt, rhodium, iridium, palladium, platinum, uranium, or rare earth metals.
 17. The method of claim 1, further comprising forming at least a portion of a heap with the agglomerated metal-bearing material after the step of agglomerating.
 18. The method of claim 17, wherein the leaching comprises leaching the heap with the leaching solution.
 19. The method of claim 1, wherein the agglomerating comprises curing the metal-bearing material in the agglomeration solution to form a cured metal-bearing material.
 20. A method for recovering a metal value from a metal-bearing material, comprising: agglomerating the metal-bearing material with an agglomeration solution to form an agglomerated metal-bearing material, wherein the agglomeration solution includes a raffinate and hydrogen peroxide; forming at least a portion of a heap with the agglomerated metal-bearing material; leaching the heap with a leaching solution to produce a pregnant leaching solution, wherein the leaching solution includes the raffinate and citric acid; and recovering the metal value from the pregnant leaching solution to produce the raffinate. 